OP, if I were you I would speak to your health visitor ASAP, to any other medical professional you are still seeing from the hospital, and also to your parents/close family/ close friends. You really need their support right now. You are vulnerable, living in someone else's space and you are being treated badly. It doesn't sound like these people have your interests at heart.
I have never said this on Mumsnet before, but I'd seriously consider staying with trusted friends and family for a while so they can support you and look after you. You've been through a lot, you've done so amazingly well caring for your babies, but you need support and care as well, and you are not getting it where you are.
After that, I would consider doing anything you can to find permanent accommodation in your own space away from your in laws, whether that is with your partner or not. The current set up might well see you bullied for the rest of your maternity. This is a special time to enjoy your babies and bond with them. You should be free to enjoy it, not battling stress, and anxiety.
Please don't listen to the people who "don't understand what the problem is", "see no big deal", "they're only in the next room", "you are lucky to have involved grandparents", "you'll need childcare from them later" etc. Your biological need to have the babies with you is entirely normal. Maybe not everyone experiences it, but many do, and it is perfectly valid. It is also very important for EBF babies for picking up hunger cues, building milk supply etc.
I still remember my son just wouldn't stop crying one time during my parents' visit and I had enough, marched up, and picked him up from them. He immediately calmed down. My mother kept saying she didn't understand, what did he need, she'd been trying everything to soothe him. The answer was very obviously "his mother"!!!